A tandem-type image forming apparatus based on the intermediate transferring scheme includes: processing units such as a process unit including a photoreceptor drum, a developing unit including a developer bearing member, and an exposure unit including an exposure member; and an intermediate transfer unit including an intermediate transfer roller. When these units are mounted on a main body of the apparatus separately, the apparatus has to have a space between the developing unit, the intermediate transfer unit and the photoreceptor drum so as to avoid flaws on the photoreceptor drum. This may degrade relative positional precision between these units and so degrade the quality of images due to color registration error.
Then, an image forming apparatus is known, which includes a unit assembly including a plurality of processing units that are attached to a tray for jointing (for example, see Patent Literature 1). Such a conventional image forming apparatus including a unit assembly is configured so that the plurality of processing units as a unit assembly is integrally inserted/removed with respect to the main body of the apparatus. The intermediate transfer unit of this apparatus is fixed to the main body of the apparatus.